JP2015018819A - Active material and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high capacity active material excellent in the charge and discharge characteristics at high potential.SOLUTION: A lithium ion secondary battery having a layer structure, and a composition represented by following formula (1) satisfies a following formula (2), where S is a specific surface area calculated by BET measurement, Dis a primary grain size corresponding to a circle calculated from the specific surface area, and Dis an average primary grain size corresponding to a circle determined from the SEM image. LiNiCoMnMO...(1)(In the formula (1), M is at least one element selected from a group consisting of Si, Ba and V, and 1.9≤(a+b+c+d+y)≤2.1, 1.05≤y≤1.3, 0<a≤0.3, 0≤b≤0.25, 0.3≤c≤0.7, 0<d≤0.1, 1.90≤x≤2.1), 3.57≤D/D≤5.39 ...(2).

Description

  The present invention relates to an active material and a lithium ion secondary battery.

  In recent years, various electric vehicles are expected to be widely used for solving environmental and energy problems. As an in-vehicle power source such as a motor driving power source that holds the key to practical application of these electric vehicles, lithium ion secondary batteries have been intensively developed. However, in order for a battery to be widely used as an in-vehicle power source, it is necessary to make the battery high performance and make it cheaper. In addition, it is necessary to make the one-mile travel distance of an electric vehicle closer to a gasoline engine vehicle, and a higher energy battery is desired.

In order to increase the energy density of the battery, it is necessary to increase the amount of electricity stored per unit mass of the positive electrode and the negative electrode. A so-called solid solution positive electrode has been studied as a positive electrode material (positive electrode active material) that may meet this demand. Among them, the solid solution of the electrochemically inactive layered Li ₂ MnO ₃ and the electrochemically active layered LiAO ₂ (A is a transition metal such as Co or Ni) exceeds 200 mAh / g. It is expected as a candidate for a high-capacity positive electrode material that can exhibit a large electric capacity (see Patent Document 1 below).

JP-A-9-55211 JP 2005-005105 A JP 2008-258160 A

However, the solid solution positive electrode using Li ₂ MnO ₃ described in Patent Document 1 has a large discharge capacity, but when used at a high charge / discharge potential, the cycle characteristics are easily deteriorated by repeated charge / discharge. There was a problem. For this reason, even a lithium ion battery using such a solid solution type positive electrode has a problem in that the cycle characteristics under high capacity use conditions are poor and the battery deteriorates immediately when charging / discharging at a high potential. On the other hand, Patent Document 2 says that good cycle characteristics can be obtained by defining the degree of bonding of the primary particles of the positive electrode material, but there is a problem that sufficient discharge capacity cannot be obtained with the composition of the above document. Further, in the positive electrode material of Patent Document 3, it is described that primary particles are fused or sintered to form secondary particles, but it is not quantified and has good cycle characteristics. There is a problem that the battery capacity is relatively small.

  The present invention has been made in view of the above-described problems of the prior art, and aims to provide an active material having a high capacity and excellent charge / discharge cycle characteristics, a method for producing the active material, and a lithium ion secondary battery. And

In order to achieve the above object, an active material according to the present invention has a layered structure, has a composition represented by the following formula (1), S is a specific surface area calculated by BET measurement, The following equation (2) is satisfied, where D _{1 is the} primary particle diameter corresponding to the circle calculated from the above and D ₂ is the average primary particle diameter corresponding to the circle determined from the SEM image.
_{Li y Ni a Co b Mn c} M d O x ··· (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.05 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 <d ≦ 0.1, 90 ≦ x ≦ 2.1. ]
3.57 ≦ D ₁ / D ₂ ≦ 5.39 (2)

The relationship of D ₁ / D ₂ described above represents the degree of neck growth of the positive electrode active material in the present invention, and the higher the value of D ₁ / D ₂ , the higher the proportion of particles growing neck. Yes. That is, by causing partial neck growth, the surface exposure of the active material can be suppressed, and a high discharge capacity and excellent cycle characteristics can be provided.

  In the active material according to the present invention, the element M is preferably Fe or V, and d is preferably 0 <d ≦ 0.1.

  Since Fe or V is an element whose valence is easily changed, there is an advantage that it is easy to maintain the crystal structure of the active material even when Li is desorbed from the active material because it moves to the negative electrode side during charging. is there.

  A lithium ion secondary battery according to the present invention includes a positive electrode current collector, a positive electrode active material layer including a positive electrode active material, a negative electrode current collector, and a negative electrode active material layer including a negative electrode active material, And a separator positioned between the positive electrode active material layer and the negative electrode active material layer, a negative electrode, a positive electrode, and an electrolyte in contact with the separator, wherein the positive electrode active material is an active material according to the present invention. Contains substances.

  The lithium ion secondary battery of the present invention containing the active material of the present invention in the positive electrode active material layer has a high capacity and hardly deteriorates in a charge / discharge cycle at a high potential.

  ADVANTAGE OF THE INVENTION According to this invention, the active material excellent in the charge / discharge cycle characteristic by a high capacity | capacitance and high potential, the manufacturing method of an active material, and a lithium ion secondary battery can be provided.

It is a schematic cross section of a lithium ion secondary battery provided with the positive electrode active material layer containing the active material formed from the precursor which concerns on one Embodiment of this invention. It is the photograph which image | photographed the active material of Example 1 with the scanning electron microscope (SEM). It is the photograph which image | photographed the active material of the comparative example 1 with the scanning electron microscope (SEM).

  Hereinafter, an active material, an active material manufacturing method, and a lithium ion secondary battery according to an embodiment of the present invention will be described. In addition, this invention is not limited to the following embodiment.

(Active material)
The active material of the present embodiment has a layered structure, has a composition represented by the following formula (1), S is a specific surface area calculated by BET measurement, and a primary equivalent to a circle calculated from the specific surface area. When the particle diameter is D ₁ and the average primary particle diameter corresponding to the circle determined from the SEM image is D ₂ , the lithium-containing composite oxide satisfies the following formula (2).
_{Li y Ni a Co b Mn c} M d O x ··· (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.05 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 90 ≦ x ≦ 2.1. ]
3.57 ≦ D ₁ / D ₂ ≦ 5.39 (2)
[However, D ₁ = 6 / (S × ρ), and ρ represents the true density of the powder calculated by BET measurement.

Note that D ₁ = 6 / (S × ρ) is obtained by converting the following equation (3), which is composed of the general formula of the volume and surface area of the particle, the true density ρ, and the surface area S of the particle obtained by BET measurement. Led by.
^{_{S = (4π (D 1/}} 2) 2) / ((4 / 3π (D 1/2) 3) × ρ) ··· (3)

Particles satisfying the above range have a structure in which primary particles are partially in contact with each other. However, if the value of D ₁ / D ₂ is too high (the value of D ₁ / D ₂ exceeds 6), the neck grows too much and the two particles sinter and become one particle. The discharge capacity may be reduced.

The layered structure is generally expressed as LiAO ₂ (A is a transition metal such as Co, Ni, and Mn), and is a structure in which a lithium layer, a transition metal layer, and an oxygen layer are stacked in a uniaxial direction. Typical examples include those belonging to the α-NaFeO ₂ type such as LiCoO ₂ and LiNiO ₂ , which are rhombohedral, and are attributed to the space group R (−3) m due to their symmetry. LiMnO ₂ is orthorhombic and is attributed to the space group Pm2m due to its symmetry. Li ₂ MnO ₃ can also be expressed as Li [Li _1/3 Mn _2/3 ] O ₂ and is a monoclinic space group C2 / m, but the Li layer and [Li _1/3 Mn _2/3 ] A layered compound in which a layer and an oxygen layer are laminated. The active material of this embodiment is a solid solution of a lithium transition metal composite oxide represented by LiAO ₂ and is a system that also allows Li as a metal element occupying a transition metal site.

(BET specific surface area S)
The calculation method of the BET specific surface area S is as follows. First, the active material powder is filled in a sample cell and previously vacuum dried at 300 ° C. for 30 minutes. Next, the sample cell is mounted on the measurement unit, and after counting the signals at the time of attachment / detachment with N2 gas, the specific surface area is calculated by the BET three-point method.

(Average primary particle diameter D ₂ )
The calculation method of the primary particle diameter of the active material is as follows. First, the active material particles are observed with a scanning electron microscope, and 500 or more primary particles are imaged. After calculating the area of the particle every single resultant image, the particle diameter in terms of circle-equivalent diameter, and the average value and D _2.

(Powder density ρ)
When the BET specific surface area is measured, not only the specific surface area S but also the density is measured at the same time, and the data is defined as the powder density ρ.

(Method for producing active material)
In the production of an active material, an active material precursor is first prepared. The precursor has a composition corresponding to the following formula (1).
_{Li y Ni a Co b Mn c} M d O x ··· (1)
In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2 .1, 1.05 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 <b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 1.90 ≦ x ≦ 2.1.

  The precursor of this embodiment includes, for example, Li, Ni, Co, Mn, M, and O, and the molar ratio of Li, Ni, Co, Mn, M, and O is similar to the composition of the above formula (1). It is a substance that is y: a: b: c: d: x. As a specific example of the precursor, a compound containing each of Li, Ni, Co, Mn, and M (for example, a salt) and a compound containing O are mixed so as to satisfy the above molar ratio, and mixed and heated as necessary. The resulting mixture. One of the compounds contained in the precursor may be composed of a plurality of elements selected from the group consisting of Li, Ni, Co, Mn, M, and O. In addition, since the molar ratio of O in the precursor varies depending on the firing conditions of the precursor (for example, atmosphere, temperature, etc.), the molar ratio of O in the precursor may be outside the numerical value range of x.

  The precursor is obtained, for example, by blending the following compounds so as to satisfy the molar ratio shown in the above formula (1). Specifically, the precursor can be produced from the following compound by a method such as pulverization / mixing, thermal decomposition mixing, precipitation reaction, or hydrolysis. In particular, a method of mixing, stirring, and heat-treating a liquid raw material in which a manganese compound, a nickel compound, a cobalt compound, and a lithium compound are dissolved in a solvent such as water is preferable. By drying this, it becomes easy to produce a complex oxide (precursor) having a uniform composition and being easily crystallized at a low temperature.

Lithium compounds: lithium acetate dihydrate, lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium chloride and the like.
Nickel compounds: nickel acetate tetrahydrate, nickel sulfate hexahydrate, nickel nitrate hexahydrate, nickel chloride hexahydrate, and the like.
Cobalt compounds: cobalt acetate tetrahydrate, cobalt sulfate heptahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, and the like.
Manganese compound: Manganese acetate tetrahydrate, manganese sulfate pentahydrate, manganese nitrate hexahydrate, manganese chloride tetrahydrate, manganese acetate tetrahydrate and the like.
M compound: Al source, Si source, Zr source, Ti source, Fe source, Mg source, Nb source, Ba source, V source (oxide, fluoride, etc.). For example, aluminum nitrate nonahydrate, aluminum fluoride, iron sulfate heptahydrate, silicon dioxide, zirconium nitrate dihydrate, titanium sulfate hydrate, magnesium nitrate hexahydrate, niobium oxide, barium carbonate, Vanadium oxide and the like.

  A raw material mixture prepared by adding a complexing agent to a solvent in which the above compound is dissolved may be further mixed, stirred, and heat-treated. In addition, if necessary, an acid may be added to the raw material mixture in order to adjust the pH. The type of complexing agent is not limited, but citric acid, malic acid, tartaric acid, lactic acid and the like are preferable in view of availability and cost.

The specific surface area of the precursor is preferably 0.5 to 6.0 m ² / g. Thereby, crystallization (sintering) of the precursor easily proceeds, and charge / discharge cycle characteristics are easily improved. When the specific surface area of the precursor is smaller than 0.5 m ² / g, the particle size of the precursor after firing (particle size of the lithium compound) becomes large, and the composition distribution of the finally obtained active material becomes non-uniform. Tend. Moreover, when the specific surface area of a precursor is larger than 6.0 m < ² > / g, the water absorption amount of a precursor increases and a baking process becomes difficult. When the water absorption amount of the precursor is large, it is necessary to prepare a dry environment, which increases the cost of manufacturing the active material. The specific surface area can be measured with a known BET type powder specific surface area measuring device. When the specific surface area of the precursor is outside the above range, the temperature at which the precursor crystallizes tends to increase. The specific surface area of the precursor can be adjusted by the grinding method, the grinding media, the grinding time, and the like.

Next, the manufactured precursor is fired. By firing the precursor, a solid solution (active material) of a lithium compound having a layered structure and represented by the following formula (1) can be obtained.
_{Li y Ni a Co b Mn c} M d O x (1)
In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2 .1, 1.05 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 <b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 1.90 ≦ x ≦ 2.1.

  The firing temperature of the precursor is preferably 800 to 1100 ° C, more preferably 850 to 1050 ° C. If the firing temperature of the precursor is less than 500 ° C., the sintering reaction of the precursor does not proceed sufficiently, and the crystallinity of the resulting lithium compound becomes low, which is not preferable. When the firing temperature of the precursor exceeds 1100 ° C., the amount of lithium evaporation increases. As a result, there is a tendency that a lithium compound having a composition lacking lithium tends to be generated, which is not preferable. On the other hand, when the temperature exceeds 1100 ° C., the primary particles are sintered with each other, and the specific surface area is remarkably reduced. If the amount of lithium added is increased, neck growth tends to occur during firing.

  The firing atmosphere of the precursor is preferably an atmosphere containing oxygen. Specific examples of the atmosphere include a mixed gas of an inert gas and oxygen, and an atmosphere containing oxygen such as air. The firing time of the precursor is preferably 3 hours or longer, and more preferably 5 hours or longer.

  In order to obtain an active material powder having a desired particle size and shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a bead mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

(Lithium ion secondary battery)
As shown in FIG. 1, a lithium ion secondary battery 100 according to the present embodiment is disposed adjacent to each other between a plate-like negative electrode 20 and a plate-like positive electrode 10 facing each other, and the negative electrode 20 and the positive electrode 10. One end is electrically connected to the negative electrode 20, a power generation element 30 including a plate-like separator 18, a nonaqueous electrolyte containing lithium ions, a case 50 containing these in a sealed state, and the negative electrode 20. A negative electrode lead 62 whose other end protrudes outside the case and a positive electrode lead 60 whose one end is electrically connected to the positive electrode 10 and whose other end protrudes outside the case. Prepare.

  The negative electrode 20 includes a negative electrode current collector 22 and a negative electrode active material layer 24 formed on the negative electrode current collector 22. The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 formed on the positive electrode current collector 12. The separator 18 is located between the negative electrode active material layer 24 and the positive electrode active material layer 14.

The positive electrode active material contained in the positive electrode active material layer 14 has a layered structure, has a composition represented by the following formula (1), S is a specific surface area calculated by BET measurement, and is calculated from the specific surface area. that if the primary particle diameter of equivalent circle was D _1, the average primary particle diameter of the equivalent circle obtained from the SEM image D2, active material and satisfies the following formula (2).
_{Li y Ni a Co b Mn c} M d O x ··· (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.05 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 90 ≦ x ≦ 2.1. ]
3.57 ≦ D ₁ / D ₂ ≦ 5.39 (2)
[However, D ₁ = 6 / (S × ρ), and ρ represents the true density of the powder calculated by BET measurement. ]

As the negative electrode active material used for the negative electrode of the lithium ion secondary battery, any material can be selected as long as it can deposit or occlude lithium ions. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

  The positive electrode active material layer 14 and the negative electrode active material layer 24 may contain a conductive agent, a binder, and the like as other components in addition to the main components.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Examples thereof include conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material. These conductive agents may be used alone, or a mixture thereof may be used. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight and more preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber. A polymer having rubber elasticity such as (SBR) or fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by weight and more preferably 2 to 30% by weight with respect to the total weight of the positive electrode active material layer or the negative electrode active material layer.

  The positive electrode active material layer or the negative electrode active material layer is a mixture obtained by kneading main constituent components and other materials into a mixture and mixing them in an organic solvent such as N-methyl-2-pyrrolidone and toluene. Is applied onto a current collector, or pressure-bonded and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. As for the application method, for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Is not to be done.

  As the current collector of the electrode, iron, copper, stainless steel, nickel and aluminum can be used. Moreover, a sheet | seat, a foam, a mesh, a porous body, an expanded lattice, etc. can be used as the shape. Further, the current collector can be used with a hole formed in an arbitrary shape.

  As the nonaqueous electrolyte, those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ (SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, Examples thereof include organic ion salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more. In particular, the active material of the present embodiment is difficult to chemically react with an electrolyte salt containing F such as LiBF ₄ , LiAsF ₆ , and LiPF ₆ and has high durability.

Further, it is preferable to use a mixture of LiPF ₆ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ . As a result, the viscosity of the non-aqueous electrolyte can be further reduced, so that the low-temperature characteristics can be further improved and self-discharge can be suppressed.

  The concentration of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, and more preferably 0.5 mol / l to 2.5 mol / l. Thereby, the nonaqueous electrolyte battery which has a high battery characteristic can be obtained reliably.

  Although the non-aqueous electrolyte has been described above, a room temperature molten salt or an ionic liquid may be used. A nonaqueous electrolyte and a solid electrolyte may be used in combination.

  As the separator 18, it is preferable to use a porous film or a nonwoven fabric exhibiting excellent high-rate discharge characteristics alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the lithium ion secondary battery separator 18 is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  As the non-aqueous electrolyte battery separator 18, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and an electrolyte may be used. Use of a nonaqueous electrolyte in a gel state has an effect of preventing leakage.

  For example, the shape of the lithium ion secondary battery is not limited to that shown in FIG. For example, the shape of the nonaqueous electrolyte secondary battery may be a square, an ellipse, a coin, a button, a sheet, or the like.

  The active material of this embodiment can also be used as an electrode material for electrochemical devices other than lithium ion secondary batteries. As such an electrochemical element, other than lithium ion secondary batteries such as a metal lithium secondary battery (an electrode containing an active material obtained by the present invention is used as a positive electrode and metal lithium is used as a negative electrode) Examples include secondary batteries and electrochemical capacitors such as lithium ion capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

Example 1
[Precursor preparation]
Lithium acetate dihydrate 39.57g, cobalt acetate tetrahydrate 5.28g, manganese acetate tetrahydrate 40.11g, nickel acetate tetrahydrate 14.47g was dissolved in distilled water and citric acid was added Then, the reaction was allowed to proceed for 10 hours while heating and stirring. The first precursor reactant was dried at 120 ° C. for 24 hours, and after removing moisture, heat-treated at 500 ° C. for 5 hours to remove organic components, thereby obtaining a tea-colored powder (precursor of Example 1). It was. In addition, lithium, nickel, cobalt contained in the precursor and the amount of lithium acetate dihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate and cobalt acetate tetrahydrate in the raw material mixture are adjusted The number of moles of manganese was adjusted to correspond to 0.3 mol of Li _1.28 Ni _0.17 Co _0.08 Mn _0.55 O ₂ . That is, the number of moles of each element in the raw material mixture was adjusted so that 0.3 mol of Li _1.28 Ni _0.19 Co _0.07 Mn _0.54 O ₂ was generated from the precursor of Example 1. . Citric acid as a complexing agent was added in an equivalent number of moles, that is, 0.3 mol with respect to 0.3 mol of the active material obtained from the precursor of Example 1.

[Production of active material]
The precursor was pulverized for about 10 minutes in a mortar and then baked in the atmosphere at 950 ° C. for 10 hours. The planetary ball mill was crushed twice at 500 rpm for 1 minute, and the lithium compound of Example 1 (active material) ) The crystal structure of the lithium compound of Example 1 was analyzed by a powder X-ray diffraction method. The active material of Example 1 was confirmed to have a rhombohedral system and a main phase having a space group R (-3) m structure. Further, in the X-ray diffraction pattern of the active material of Example 2, a diffraction peak peculiar to the Li ₂ MnO ₃ type monoclinic space group C2 / m structure was observed at 2θ of around 20 to 25 °.

(Composition analysis)
As a result of the composition analysis by the inductively coupled plasma method (ICP method), the composition of the lithium compound (active material) of Example 1 is Li _1.28 Ni _0.19 Co _0.07 Mn _0.54 O _2. confirmed. It was confirmed that the molar ratio of each metal element in the active material of Example 1 coincided with the molar ratio of each metal element in the precursor of Example 1. That is, it was confirmed that the composition of the lithium compound (active material) obtained from the precursor can be accurately controlled by adjusting the molar ratio of the metal elements in the precursor.

(BET specific surface area)
The lithium compound (active material) of Example 1 was filled in a sample cell, and was previously vacuum-dried at 300 ° C. for 30 minutes. Next, the sample cell was attached to the measurement part, and the specific surface area was calculated by the BET three-point method after counting signals at the time of attachment / detachment with N 2 gas. As a result, the specific surface area of the lithium compound of Example 1 was 0.79 m ² / g.

(SEM average particle size)
The lithium compound (active material) of Example 1 was observed with a scanning electron microscope, and 500 or more primary particles were imaged. After calculating the area of each particle of the obtained image, it was converted to the equivalent circle diameter to obtain the particle diameter, and the average value thereof was taken as the SEM primary particle diameter. As a result, the SEM primary particle size of the lithium compound of Example 1 was 0.41 μm. The primary particle SEM image of Example 1 is shown in FIG. It can be seen from FIG. 2 that the primary particles are neck-growing while maintaining their shapes.

(True powder density ρ)
As the true density ρ of the powder, the value of the true density that is simultaneously measured when measuring the BET specific surface area is used. The true density ρ of the lithium compound of Example 1 was 3.45.

[Production of positive electrode]
The positive electrode coating material was prepared by mixing the lithium compound (active material) of Example 1, a conductive additive, and a solvent containing a binder. The positive electrode coating material was applied to an aluminum foil (thickness 20 μm) as a positive electrode current collector by a doctor blade method, dried at 100 ° C., and rolled. This obtained the positive electrode comprised from the layer of a lithium compound (active material) and a positive electrode electrical power collector. Carbon black and graphite were used as the conductive assistant. As a solvent containing a binder, N-methyl-2-pyrrolidone in which PVDF was dissolved was used.

[Production of negative electrode]
A negative electrode paint was prepared in the same manner as the positive electrode paint except that natural graphite was used in place of the active material of Example 1 and only carbon black was used as the conductive additive. The negative electrode coating material was applied to a copper foil (thickness 16 μm) as a negative electrode current collector by a doctor blade method, dried at 100 ° C., and rolled. This obtained the negative electrode comprised from a negative electrode active material layer and a negative electrode electrical power collector.

[Production of lithium ion secondary battery]
The positive electrode, negative electrode, and separator (polyolefin microporous membrane) produced above were cut into predetermined dimensions. The positive electrode and the negative electrode were provided with portions to which no electrode paint was applied in order to weld the external lead terminals. A positive electrode, a negative electrode, and a separator were laminated in this order. When laminating, a small amount of hot melt adhesive (ethylene-methacrylic acid copolymer, EMAA) was applied and fixed so that the positive electrode, the negative electrode, and the separator did not shift. An aluminum foil (width 4 mm, length 40 mm, thickness 100 μm) and nickel foil (width 4 mm, length 40 mm, thickness 100 μm) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals. Polypropylene (PP) grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. This is to improve the sealing performance between the external terminal and the exterior body. An aluminum laminate material composed of a PET layer, an Al layer, and a PP layer was used as a battery outer package enclosing a battery element in which a positive electrode, a negative electrode, and a separator were stacked. The thickness of the PET layer was 12 μm. The thickness of the Al layer was 40 μm. The thickness of the PP layer was 50 μm. PET is polyethylene terephthalate and PP is polypropylene. In producing the battery outer package, the PP layer was disposed inside the outer package. A battery element was placed in the outer package, an appropriate amount of electrolyte was added, and the outer package was vacuum-sealed. Thereby, a lithium ion secondary battery using the lithium compound of Example 1 was produced. As the electrolyte solution, were used as the LiPF ₆ in a mixed solvent of ethylene carbon sulfonate (EC) and dimethyl carbonate (DMC) was dissolved at a concentration 1M (1mol / L). The volume ratio of EC to DMC in the mixed solvent was EC: DMC = 30: 70.

[Measurement of electrical characteristics]
The manufactured lithium ion secondary battery was charged at a constant current of 30 mA / g to 4.8 V at a current value, and then discharged at a constant current of 2.0 mA at a current value of 30 mA / g. The discharge capacity of Example 1 was 205 mAh / g. A cycle test was repeated for 50 cycles of this charge / discharge cycle. The test was conducted at 25 ° C. Assuming that the initial discharge capacity of the battery of Example 1 was 100%, the discharge capacity after 50 cycles was 99%. Hereinafter, the ratio of the discharge capacity after 50 cycles when the initial discharge capacity is 100% is referred to as cycle characteristics. High cycle characteristics indicate that the battery is excellent in charge / discharge cycle characteristics. A battery having a capacity of 190 mAh / g or more and a cycle characteristic of 85% or more is evaluated as “A”. A battery having a capacity of less than 190 mAh / g or a cycle characteristic of less than 85% is evaluated as “F”.

(Examples 2-4, Comparative Examples 1-6)
In Examples 2 to 4 and Comparative Examples 1 to 6, lithium compounds were prepared by changing the firing temperature of the precursor and the subsequent crushing conditions.

  In Example 2, the precursor was pulverized for about 10 minutes and then calcined at 950 ° C. for 10 hours, and planetary ball mill crushing was performed four times at 500 rpm for 1 minute to obtain a lithium compound.

  In Example 3, the precursor was pulverized for about 10 minutes and then calcined at 900 ° C. for 10 hours, and planetary ball mill crushing was performed twice at 500 rpm for 1 minute to obtain a lithium compound.

  In Example 4, the precursor was pulverized for about 10 minutes and then calcined at 900 ° C. for 10 hours, and planetary ball mill crushing was performed twice at 500 rpm for 1 minute to obtain a lithium compound.

In Comparative Example 1, the precursor was pulverized for about 10 minutes and then calcined at 1050 ° C. for 10 hours. The planetary ball mill was crushed nine times at 500 rpm for 1 minute to obtain a lithium compound. It was 1.45 m < ² > / g when the BET specific surface area of the said lithium compound was measured. The SEM primary particle size was 0.42 μm. The primary particle SEM image of the comparative example 1 is shown in FIG. Although the SEM primary particle sizes in FIGS. 2 and 3 are approximately the same, the BET values are greatly different, and it was found that the lithium compound of Comparative Example 1 has a large degree of neck growth. This can be judged by comparing the images of FIG. 2 and FIG. 3 and having a small particle irregularity (contrast between light and shadow in the image).

  In Comparative Example 2, the precursor was pulverized for about 10 minutes and then calcined at 950 ° C. for 10 hours, and planetary ball mill crushing was performed 7 times at 500 rpm for 1 minute to obtain a lithium compound.

  In Comparative Example 3, the precursor was pulverized for about 10 minutes, then calcined at 900 ° C. for 10 hours, and planetary ball mill crushing was performed 7 times at 500 rpm for 1 minute to obtain a lithium compound.

  In Comparative Example 4, the precursor was pulverized for about 10 minutes and then calcined at 1100 ° C. for 10 hours to obtain a lithium compound.

(Examples 5 to 10)
In Examples 5 to 10 and Comparative Examples 5 and 6, the amounts of Co source, Ni source, and Mn source in the precursor raw material mixture were adjusted, and the precursor was pulverized for about 10 minutes, and then at 950 ° C. for 10 hours. After firing, planetary ball mill crushing was performed twice at 500 rpm for 1 minute to obtain a lithium compound.

(Examples 11 to 19)
In Examples 11 to 19, lithium compounds were obtained by adjusting the composition of the precursor raw material mixture. That is, as the source of M represented by the formula (1), in Example 11, aluminum nitrate nonahydrate was used as the Al source in the precursor raw material mixture. In Example 12, vanadium oxide was used as a V source in the precursor raw material mixture. In Example 13, silicon dioxide was used as the Si source in the precursor raw material mixture. In Example 14, magnesium nitrate hexahydrate was used as the Mg source in the precursor raw material mixture. In Example 15, zirconium oxide dihydrate was used as a Zr source in the precursor raw material mixture. In Example 16, titanium sulfate hydrate was used as a Ti source in the precursor raw material mixture. In Example 17, iron sulfate heptahydrate was used as the Fe source in the precursor raw material mixture. In Example 18, barium carbonate was used as the Ba source in the precursor raw material mixture. In Example 19, niobium oxide was used as the Nb source in the precursor raw material mixture. These precursors were pulverized for about 10 minutes and then calcined at 950 ° C. for 10 hours, and planetary ball mill crushing was performed twice at 500 rpm for 1 minute to obtain a lithium compound.

  In the same manner as in Example 1, the discharge capacities and cycle characteristics of the batteries of Examples 2 to 19 and Comparative Examples 1 to 4 were evaluated. The results are shown in Table 1. In the following table, a battery having a capacity of 190 mAh / g or more and a cycle characteristic of 85% or more is evaluated as “A”. A battery having a capacity of less than 190 mAh / g or a cycle characteristic of less than 85% is evaluated as “F”.

The compositions of the active materials in Examples and Comparative Examples were as shown in Table 1. It was confirmed that the compositions of Examples 1 to 19 and Comparative Examples 1 to 4 were within the range of the following formula (1).
_{Li y Ni a Co b Mn c} M d O x ··· (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Al, Si, Zr, Ti, Fe, Mg, Nb, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.05 ≦ y ≦ 1.3, 0 <a ≦ 0.3, 0 <b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 ≦ d ≦ 0.1, 9 ≦ x ≦ 2.1. ]

Table 1 shows the D ₁ / D ₂ of the active materials of Examples and Comparative Examples. Examples 1 to 19 were confirmed to be within the range of the following formula (2).
3.57 ≦ D ₁ / D ₂ ≦ 5.39 (2)
On the other hand, it was confirmed that Comparative Examples 1-4 did not enter into the range of the above formula (2).

  The initial discharge capacity and cycle characteristics of the batteries using the active materials of Examples 1 to 19 are as shown in Table 1. Both have a discharge capacity of 190 mAh / g or more and a cycle characteristic of 85% or more. Was confirmed.

  The initial discharge capacity and cycle characteristics of the batteries using the active materials of Comparative Examples 1 to 4 are as shown in Table 1, both of which have a discharge capacity of less than 190 mAh / g or a cycle characteristic of less than 85%. It was confirmed.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 20 ... Negative electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 22 ... Negative electrode collector, 24 ... Negative electrode Active material layer, 30 ... power generation element, 50 ... case, 60, 62 ... lead, 100 ... lithium ion secondary battery.

Claims (3)

Has a layered structure,
It has a composition represented by the following formula (1),
When the specific surface area calculated by BET measurement is S, the primary particle diameter corresponding to the circle calculated from the specific surface area is D ₁ , and the average primary particle diameter corresponding to the circle calculated from the SEM image is D ₂ , the following formula ( An active material characterized by satisfying 2).
_{Li y Ni a Co b Mn c} M d O x ··· (1)
[In the above formula (1), the element M is at least one element selected from the group consisting of Si, Ba and V, and 1.9 ≦ (a + b + c + d + y) ≦ 2.1, 1.05 ≦ y ≦ 1. 3, 0 <a ≦ 0.3, 0 ≦ b ≦ 0.25, 0.3 ≦ c ≦ 0.7, 0 <d ≦ 0.1, 1.90 ≦ x ≦ 2.1. ]
3.57 ≦ D ₁ / D ₂ ≦ 5.39 (2)
[However, D ₁ = 6 / (S × ρ), and ρ represents the true density of the powder calculated by BET measurement. ]   The active material according to claim 1, wherein the element M in the formula (1) is V. A positive electrode having a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material;
A negative electrode having a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material;
A separator positioned between the positive electrode active material layer and the negative electrode active material layer;
An electrolyte in contact with the negative electrode, the positive electrode, and the separator,
The positive electrode active material includes the active material according to claim 1,
Lithium ion secondary battery.